1. Field of the Invention
The present invention relates to a programmable frequency divider.
2. Prior Art
Hitherto, a programmable counter constituted by a down counter of a preset-type or an up counter of a reset-type has been used as a programmable frequency divider. However, as is well known, a normal programmable counter could change the program value by only one clock pulse unit. Therefore in a case where a nominal output frequency of the programmable frequency divider is 2,000 Hz and its output frequency is required to be changed by about 1 Hz unit, a nominal dividing value of 2,000 is needed and the frequency of the clock pulse required is 4 MHz.
This kind of programmable frequency divider has been used as a part of a frequency synthesizer in rotation control apparatus of a record player or in a citizen band (CB) radio transceiver. In this kind of apparatus, since the whole of the electric circuit is rather complex and large in scale, a principal circuit including the programmable frequency divider is very often constructed by a one-chip LSI (Large Scale Integration) IC, or alternatively, at least by a digital MSI (Medium Scale Integration) IC for general use. The power consumption of these digital ICs usually increases in proportion to a rise in the frequency of the clock pulse. For example, in a CMOS-IC (Complementary Metal Oxide Semicondutor IC) which is suitable for large scale integration, current consumption increases in proportion to the rise in the frequency of the clock pulse and in IIL-IC (Integrated Injection Logic IC), it is necessary to effect a preliminary amplification of an injection current when use of a clock pulse of high frequency is intended.
An increase in power consumption necessitates an electric power source of a large capacity. Also the life time of a battery such as a dry battery in a portable apparatus is shortened, and the high power consumption increases the amount of heat produced in the circuit components. This lowers the reliability of the apparatus and also prevents a miniturization of the package into a one-chip LSI.